Method and apparatus for conducting a process in a pulsating environment

ABSTRACT

An improved flame holder based tunable pulse combustor, and a processing system employing same. The processing system is for thermal, chemical, and physical processes which employ natural acoustic modes in a processing chamber to enhance the processing. An acoustically resonant processing chamber is provided as the processing vessel. A frequency tunable pulse combustor comprising a flame holder is positioned to excite natural acoustic modes in the processing chamber. Material introduced into the processing chamber is thereby subjected to acoustic pulsations while the material is being processed. The acoustic excitations in the system result in improved moisture removal and particle heating. Also disclosed are various embodiments of frequency and amplitude tunable pulse combustors which may be employed to excite the natural acoustic modes in the processing chamber, including axially translatable acoustic decoupler and flame holder configurations.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of U.S. Pat. application Ser. No. 075,065filed July 17, 1987, Pat. No. 4,770,626 which is a divisional of U.S.Pat. application Ser. No. 836,997 filed Mar. 6, 1986, which issued onOct. 13, 1987 as U.S. Pat. No. 4,699,588.

TECHNICAL FIELD

The present invention relates generally to pulse combustion andacoustics, and more specifically to a use of natural acoustic modes in aprocessing chamber induced by pulsating sources such as tunable pulsecombustors, oscillatory combustion in shear layers, fuel modulation andthe like, to enhance a chemical, a thermal or a physical process. Thepresent invention particularly relates to an improved, tunable pulsecombustor apparatus which can be used as an acoustic excitation means.

BACKGROUND OF THE INVENTION

In many industrial chemical, thermal and physical processing systems,burners are used to produce gas streams having specific temperatures andcompositions for a variety of applications involving momentum, heatand/or mass transfer processes. The costs of many of these materialprocessing applications could be reduced if practical means forenhancing the rates of momentum, heat and mass transfer could be found.There is evidence in the prior art that the presence of pulsations in agas flow results in large increases in the rates of momentum, heat andmass transfer processes.

Pulse combustors are known in the art as highly efficient sources ofhigh temperature pulsating gas streams for heaters, boilers, and thelike. Consequently, operational and capital investment costs of manyindustrial processes could be reduced if steady state burners commonlyemployed in such systems were replaced by pulse combustors which producepulsating flows having the required thermal loads, temperature andcompositions.

However, prior to the present invention pulse combustors were notoptimally used in various industrial processes such as drying,calcining, heating and the like. Furthermore, prior to the presentinvention it has not been believed that pulse combustors could bedesigned to possess large turndown ratios, operate efficiently over wideranges of fuel/air ratios and possess capabilities for controlling theamplitudes and frequencies of their pulsations. For example, in oneprior art pulse dryer presently used for drying a slurry of kaolin, theslurry of material to be dried is injected directly into the tail pipeof a pulse combustor a short distance upstream of the pulse combustorexit plane. Upon leaving the pulse combustor, the pulsating flow andinjected material enter a primary cyclone or drying chamber. Theinjection of material into the combustor tail pipe interferes with thecombustor operation by adversely affecting its acoustic characteristics.This, in turn, limits the amount of material which can be dried andworsens the combustion process by decreasing the combustor capacity toingest combustion air and achieve adequate mixing between the fuel andair. This results in incomplete combustion and undesirable sootformation in the combustor which adversely affects the properties ofdried material, such as kaolin. Moreover, in this system the pulsationsfrom the pulse combustor are damped out in the drying chamber, and noadvantage whatsoever is taken of the natural acoustic characteristics ofthe drying chamber.

Other prior art material drying systems are known to use pulsecombustors. In U.S. Pat. No. 3,618,655 to Lockwood, a paste of slurry ofmaterial to be dried is introduced into the exhaust pipe of a pulse jetengine, and the partly dried particles are then dispensed into a tankhaving vortices of gas at a substantially lower temperature than thatfound in the pulse jet exhaust. This structure is similar to theabove-described kaolin drying system, and also appears unconcerned withthe natural acoustic characteristics of the drying volume. In addition,there is a risk of overheating (with resultant burning of organicmaterials such as food products) in this type system, since the materialis injected directly into the hot gas flow. Also, the system uses selfaspirating pulse combustors which have limited ranges of operatingconditions.

It is also known in the art to synchronize an oscillation-radiationchamber of a furnace with a pulsating combustion chamber. For example,in the papers of F. H. Reynst, there is described a system which employsa plurality of pulse combustors to excite a longitudinal acoustic modeinside a furnace chamber. By increasing or shortening the length of theoscillating column in the pulse combustors, the frequency is altered,thereby altering the oscillation induced in the radiation chamber. Thissystem, however, appears limited to excitation of longitudinal acousticmodes in the furnace chamber. Moreover, the problems encountered inmaterial processing environments, such as temperature, composition andmoisture control and material drying time which are critical in, forexample, dryers and calciners, are not considered in Reynst's writings.

It is also known in the art that transverse or "sloshing" type acousticoscillations can be excited in cylindrical chambers and combustors. Forexample, the phenomenon of transverse oscillations was observed instudies of transverse instabilities in liquid fuel rocket motors.

It is also known in the art that undesirable acoustic oscillations,generally known as combustion instabilities, can be excited in ramjets,jet engine afterburners, solid propellant rocket motors and otherpropulsion systems by combustion processes inside shear layers whichform downstream of flame holders, corners and mechanical obstacles. Instudies directed towards the elimination of these undesirable combustioninstabilities by, for example, Schadow and coworkers and Heitor et al.,it has been shown that these instabilities are caused by interactionsbetween vortex shedding at the origin of the shear layer, acousticmotions inside the propulsive device and unsteady combustion withinvortices which are convected by the flow inside the shear layer. In allof these studies the investigated acoustic oscillations were restrictedto the combustor under study and no teachings were provided as to howsuch pulsations can be used to improve industrial processes.

Prior to the present invention, however, there has been no attempt toutilize unsteady combustion processes inside shear layers, similar tothose which excite undesirable combustion instabilities in propulsionsystems, to excite flow pulsations within a processing chamber whichwill improve the rates of mass, momentum and heat transfer between theprocessed material and processing medium. Also, there has been nosuccessful teaching that natural acoustic modes can be excited in avolume or system, such as a processing chamber, located downstream ofthe shear layer combustion region by an interaction between the acousticmode oscillations excited inside the downstream volume and unsteadycombustion within the shear layer. Also, prior to the present invention,there has been no teaching in the literature on how to construct pulsecombustors which utilize unsteady combustion inside one or more shearlayers to excite flow pulsations, and how to utilize such combustors toexcite different acoustic mode oscillations in a processing chamber towhich they are attached.

SUMMARY OF THE INVENTION

The present invention overcomes the above-described and other problemsin prior art material and other processing systems by taking advantageof the natural acoustic modes of a processing chamber. Brieflydescribed, the present invention comprises an improved pulsatingmaterial processing system which employs natural acoustic modes of aprocessing chamber to enhance the processing of the material byimproving the rates of heating, mixing and mass transfer, temperaturecontrol, moisture control, composition control, and control of materialdrying time. The present invention is useful in both chemical, thermaland physical material processing systems, such as calciners, industrialdryers, boilers, furnaces, ovens and the like.

In preferred embodiments of the present invention, an acousticallyresonant processing chamber is provided for processing materialintroduced into the processing chamber. A pulse combustor is providedfor introducing a flow of heated gases into the processing chamber toprocess material introduced into the processing chamber. If necessary,cold dilution air is added to control the processing chambertemperature. Finally, means for exciting at least one natural acousticmode in the processing chamber is provided so that material introducedinto the processing chamber is subjected to acoustic pulsations whilethe material is being processed. Advantageously, the rates of heat,mass, and momentum transfer to and from the material are improved by thesubjection of the processed material to these acoustic pulsations.

More particularly described, in the present invention, particularacoustic modes such as longitudinal, tangential, radial,tangential-radial, and three-dimensional modes are selectively excitedby selective positioning of an acoustic exciter which is frequencytunable. These modes, which may include any longitudinal, transverse orthree-dimensional mode of the processing system, may be selected inorder to optimize certain parameters of the process such as drying orchemical reaction rates or to increase the length of the path of travelof material in the processing chamber. In the preferred embodiments, thefrequency tunable acoustic exciter is a tunable pulse combustor,although other equally suitable exciting means are disclosed.

For many applications to derive maximum benefit from these acousticoscillations, the acoustic exciter must be tuned to one or more of thenatural acoustic modes of the processing chamber. Various configurationsfor tuning to these natural acoustic modes are provided. In the variousembodiments disclosed, the tuning of the processing chamber iseffectuated by the interaction between the natural acoustic modeoscillations in the processing chamber and the unsteady combustionprocesses inside one or more shear layers, such as the shear layerswhich form downstream of a circular disc flame holder, a conical flameholder, a rod flame holder, a ring flame holder, a combination of ringand rod flame holders, corner flame holders and the like. Tuning is alsoeffectuated by interaction between unsteady combustion processes in theshear layer and acoustic modes oscillations in both the processingchamber and in the region upstream of the flame holder. Tuning is alsoeffectuated by positioning the flame holder at different locationswithin the combustor, by selection of flame holder and combustor sizes,and by positioning of the flame holder within the processing chamber.Also, a combination of flame holders, placed in different positionswithin the combustor and/or the processing chamber can be employed tocontrol the frequency and amplitude of the excited processing chamberpulsations.

Still more particularly described, a plurality of frequency-tunablepulse combustors are employed to excite the acoustic mode oscillationsin the processing chamber. These pulse combustors are mounted inparticular geometric arrays to excite longitudinal, transverse orthree-dimensional oscillations. One preferred frequency tunable pulsecombustor comprises a combustor tube which includes a flame holdingdevice and a shear layer region which forms downstream of the flameholder. Unsteady reaction of fuel and air occurs within convectedvortices inside the shear layer region. The unsteady combustion producesunsteady heat release and unsteady gas expansion which excite acousticmode oscillations inside the combustor and the processing chamber. Yetanother preferred combustor embodiment comprises a combustor tube whichincludes a flame holding device and a shear layer wherein reaction offuel and air occurs and heat is released within the shear layer whichexcites one or more natural acoustic modes within the processing chamberonly. In most configurations, an air intake supplies combustion air intothe combustion zone for reaction, and fuel injectors supply fuel intothe combustion zone. Hot gases are exhausted from the combustor tube byexhaust means. The frequency of pulsating combustion is controlled byaltering the flame holder (such as its position or size), the acousticcharacteristics of the combustor, or both, so as to provide aselectively variable or tunable frequency of pulsating combustion.

Various means are disclosed for altering the acoustic characteristics ofthe combustor tube. In one disclosed embodiment, the combustor tubecomprises an axially translatable interfitting sleeve which is moved toalter the length of the combustor tube. In another embodiment the backwall of the combustor translates axially, thereby also affecting thelength of the combustor tube. In another embodiment, one of the fuelinjectors is axially translatable, and is adjusted to position thecombustion zone to excite pulsations with a desired frequency in thecombustor. In another embodiment, the flame holder is axiallytranslatable, and is adjusted to position the combustion zone to excitepulsations with a given frequency. In yet another embodiment, the sizeof flame holder is changed to excite pulsations with a desiredfrequency. In yet another embodiment, the geometry of the flame holderis changed to excite pulsations with a given frequency. In yet anotherembodiment, several flame holders are used to excite pulsations of agiven frequency. Advantageously, the use of the tunable pulse combustorsto excite one or more natural acoustic resonances in the processingchamber combines the functions of an energy source and a soundexcitation means within a single device.

Other embodiments of the tunable pulse combustor include fuel or airflow modulation for providing fuel or air to the combustion zone at aselectively variable frequency and the provision of primary andsecondary fuel or air supplies to the combustion zone, one modulated andone unmodulated.

Yet still more particularly described, the acoustic modes excited in theprocessing chamber include its natural longitudinal, transverse andthree-dimensional acoustic modes. Longitudinal modes include modeswherein oscillations occur along the axis of the processing chamber andthe properties of the oscillations are uniform at each axial location.Transverse modes include the radial modes, wherein oscillations occurabout a geometric center and along radii of a cylindrical processingchamber, as well as tangential modes, wherein oscillations occur in a"sloshing" or circumferential manner along specific paths in thetransverse plane of a cylindrical processing chamber, andtangential-radial modes wherein oscillations occur along both radial andthe specific paths of the tangential mode in the transverse plane of acylindrical processing chamber. Three-dimensional mode oscillationsinclude oscillations consisting of a combination of motions exhibited byone of the longitudinal and one of the transverse modes. Advantageously,arrangements of the acoustic exciting means in a particularpredetermined array and operating them at a specific frequency canexcite any desired mode, or a plurality of modes simultaneously, such assimultaneous excitation of a transverse and a longitudinal mode.Material subjected to the oscillations experiences a high degree ofacoustic excitation which controls particle and gaseous dispersion aswell as heat, mass and momentum transfer to and from the material.

Accordingly, it is an object of the present invention to provide a novelpulsating processing apparatus and method which utilizes the excitationof acoustic waves to improve heat, momentum and mass transfer processes,and increase process output and thermal efficiency.

It is another object of the present invention to reduce operating costsin a material processing system by enhancing the rates of heat, momentumand mass transfer.

It is another object of the present invention to provide improved pulsecombustors and material processing systems which save energy due toincreased efficiencies of operation.

It is another object of the present invention to provide an improvedpulsating processing system which employs acoustic oscillations in achemical, thermal, or physical material processing system to increaseoutput of the process.

It is another object of the present invention to provide an improvedpulsating processing system which includes means for selectivelyexciting acoustic modes in a processing system to take advantage of thenatural acoustic modes of a processing chamber.

It is another object of the present invention to provide an improvedslurry material dryer which utilizes longitudinal, transverse orthree-dimensional acoustic oscillations in a drying chamber to promoteand enhance drying.

It is a particular object of the present invention to provide animproved drying apparatus for color sensitive materials such as kaolinand organic materials such as food products and pharmaceuticals.

It is another object of the present invention to provide an improvedpulse combustor with improved operational range.

It is another object of the present invention to provide an improvedpulse combustor which is frequency tunable so that it may besuccessfully employed to excite various acoustic modes in furnaces orother processing chambers with which such combustors may be used.

It is another object of the present invention to provide an improvedpulse combustor which is frequency tunable.

It is another object of this invention to provide an improved pulsecombustor design which consists of a straight pipe and a flame holder.

It is another object of the present invention to provide an improvedpulse combustor which possesses independent means to control the air andfuel flow rates, locations of air and fuel injection into the combustor,the location of the flame holder and the geometry of the flame holder,to enable optimization of the characteristics of the combustor, such asoperation over wide ranges of fuel/air ratios and fuel inputs to controlthe energy content, composition, temperature, amplitude and frequency ofpulsations of the combustor exhaust flow.

It is another object of the present invention to provide an improvedindustrial material processing system such as an industrial dryer whichdoes not require injection of material to be dried into the exhaust flowof a pulse combustor, thereby undesirably affecting the operation of thepulse combustor.

It is another object of the present invention to provide an improvedindustrial material processing system such as an industrial dryerwherein the drying rate can be controlled by controlling the path lengthof material through the system with oscillatory movement of thematerial.

These and other objects, features, and advantages of the presentinvention may be more clearly understood and and appreciated from areview of the following detailed description of the disclosedembodiments and by reference to the appended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view, in cross section, of a materialprocessing system according to a preferred embodiment of the presentinvention, wherein a pair of tunable pulse combustors are employed toexcite a tangential acoustic mode in a processing chamber.

FIG. 2, consisting of FIG. 2A and FIG. 2B, comprises schematic endviews, in cross section, of the preferred embodiment of FIG. 1, showingpressure and flow stream lines in the processing chamber when its firsttangential mode is excited.

FIG. 3 is a schematic side view, in cross section, of another embodimentof a material processing system constructed in accordance with thepresent invention, wherein the processing chamber is operated at anangular inclination.

FIG. 4 is a schematic end view, in cross section of the embodiment ofFIG. 3, illustrating the tumbling path or trajectories of material inthe system.

FIG. 5 illustrates the instantaneous pressure and flow stream linesoscillations of the first tangential mode of a cylinder at the beginningand midway of a period of oscillation.

FIG. 6, consisting of FIGS. 6A and 6B, illustrates first and secondtangential modes of oscillation.

FIG. 7, consisting of FIGS. 7A and 7B, illustrates first and secondradial modes of oscillation.

FIG. 8, consisting of FIGS. 8A and 8B, illustrates first and secondlongitudinal modes of oscillation.

FIG. 9 is another schematic end view, in cross section, of a cylindricalprocessing chamber illustrating placement of combustors or otheracoustic exciting means to excite tangential and other acoustic modes.

FIG. 10, consisting of FIGS. 10A and 10B, comprises schematic end andside views, in cross section, of a cylindrical processing chamberillustrating placement of combustors or other acoustic exciting means toexcite radial and other acoustic modes.

FIG. 11 comprises schematic end and side views, partly in cross section,of a cylindrical processing chamber illustrating placement of combustorsor other acoustic exciting means to excite longitudinal and otheroscillations.

FIG. 12 is a schematic view, in cross section, of an alternateembodiment of the material processing system of FIG. 1, employing ashort combustor and a disc type flame holder attached to a translatablerod used to excite acoustic mode oscillations inside the processingchamber.

FIG. 13 is a partial schematic side view, in cross section, of yetanother embodiment of a material processing system constructed inaccordance with the present invention, wherein a constant flow rate airstream and a modulated flow rate fuel stream are supplied directly tothe processing chamber and employed to excite a periodic combustionprocess and acoustic mode oscillations of desired frequency inside theprocessing system.

FIG. 14 is a detailed side view, partly broken away, of therotating-sleeve fuel flow modulator employed in the embodiment of FIG.13.

FIG. 15 is a schematic view, in cross section, of a preferred embodimentof a tunable, variable length, straight pipe, pulse combustor with atranslatable, open upstream end attached to a decoupler and a discshaped flame holder attached to a centerbody which can be translatedalong the combustor.

FIG. 16 is a schematic view, in cross section, of another preferredembodiment of a tunable, variable length, straight pipe, pulse combustorwith a translatable, closed upstream end and a disc shaped flame holderattached to a centerbody which can be translated along the combustor.

FIG. 17 is a schematic view, in cross section, of another preferredembodiment of a tunable pulse combustor which utilizes the corner at theinterface between the air inlet and the combustor and a disc shapedflame holder attached to a translatable centerbody to generate two shearlayers which interact with one another.

FIG. 18 is a schematic view, in cross section, of another preferredembodiment of a tunable, straight pipe, pulse combustor with atranslatable, open upstream end, which utilizes a flat annular ringattached to the pipe's inner wall and a translatable, disc shaped, flameholder to generate two shear layers which interact with one another.

FIG. 19 is a schematic view, in cross section, of another preferredembodiment of a tunable, straight pipe, pulse combustor with atranslatable, open upstream end, which utilizes a ring attached to thecombustor tube wall and a disc welded to the downstream termination of atranslatable centerbody to generate two shear layers which interact withone another.

FIG. 20 is a schematic view, in cross section, of another preferredembodiment of a tunable, straight pipe, pulse combustor with atranslatable, open upstream end, which utilizes a circular ring flameholder attached by thin metal rods to the outer combustor tube wall anda ring flame holder attached to a translatable centerbody to generatetwo shear layers which interact with one another.

FIG. 21 is an end view of the two ring type flame holders shown in FIG.20.

FIG. 22 illustrates a conical flame holder.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, in which like numerals indicate likeelements throughout the several views, and more particularly to FIG. 1thereof, a preferred embodiment of a material processing system 10constructed in accordance with the present invention is illustrated. Thesystem 10 includes a generally cylindrical processing chamber 12 and apair of pulse combustors 14a, 14b connected at the upper end 13 toexcite, for example, transverse oscillations in the processing chamber(see FIG. 2). In particular, the illustrated system 10 is a dryerapparatus adapted for drying a slurry of wet material, such as kaolin,introduced through a supply pipe 16 which is preferably aligned with anacoustic pressure nodal line and injected downwardly into the upper end13 of the processing chamber 12 through a plurality of nozzles or valves17. If required, dilution air may be introduced through a dilution airinlet 18 to reduce the temperature in the processing chamber to adesired level.

The processing chamber 12 also includes a closed top 20 and afrustoconical collection zone 21 wherein dried material 15 is depositedafter experiencing acoustic pulsations throughout its residence time inthe dryer. An auger-type removal system 22 is employed to remove thedried material 15 from the collection zone 21.

Generally, the exhaust means for the processing chamber should bepositioned near pressure nodes of excited oscillations to minimizeinterference with the oscillations. Exhaust gases from the system 10 ofthe preferred embodiment therefore exit via a radially-extending exhaustport 25. The exhaust gases in the preferred embodiment are drawn into aport 23 by a negative pressure created by an exhaust fan (notillustrated), and thence into a longitudinally extending and axiallypositioned exhaust pipe 24. Exhaust gases drawn into the exhaust pipe 24are vented from the processing chamber through the exhaust port 25 whichdirects the exhaust gases out of the system. The exhaust pipe 24 istherefore preferably positioned along an axis of the cylinder of theprocessing chamber 12 since the axis is closest to pressure nodes oftangential modes of oscillation, therefore only minimally interferingwith the oscillations of these modes in the processing chamber.

As material is introduced into the top of the processing chamber 12, andfalls downwardly through the processing chamber under the influence ofgravity, the material experiences tangential acoustic pulsations in eachhorizontal plane in the dryer in the embodiment of FIG. 1.Advantageously, the material to be dried is not injected directly intothe exhaust stream emanating from the pulse combustors 14a, 14b, andtherefore do not interfere with the pulse combustor operation. Thedrying time of the material can be controlled by varying the dryerlength L, inclination angle α of the dryer, and characteristics ofexcited pulsations.

The pulse combustors 14a, 14b in FIG. 1 are mounted to the processingchamber 12 so as to excite transverse acoustic oscillations in theprocessing chamber. As can best be seen in FIG. 2, the pulse combustorsare operated as a tandem pair and are mounted to exhaust gases fromexhaust region 30a, 30b of the combustors and along an interiorcircumference of the processing chamber 12. Pulse combustors 14a and 14bin FIG. 1 will also excite oscillations of longitudinal orthree-dimensional modes of the processing chamber 12 when operated atthe frequencies of these modes. It will therefore be understood thatexcitation of various acoustic modes is substantiallyfrequency-sensitive.

FIG. 3 illustrates a second preferred embodiment 10' wherein theprocessing chamber 12' is placed at an angle α. In this embodiment, thepulse combustors 14a', 14b' are operated to impart a spiral, tumblingmotion to material introduced into the system through injection valves17', as shown in FIG. 4, which are positioned diametrically opposite theexhaust outlets 30' of the combustors 14'. The exhaust entry port 23' ispositioned along an axis of processing chamber, aligned with thepressure nodes of the tangential acoustic modes.

The combined effects of gravity and pulsating tangential velocityoscillations in the angularly inclined processing chamber 12' willproduce a "tumbling" spiral flow in the processing chamber. As shown inFIG. 4, the processed particles will be periodically urged alongtangential paths inside the processing chamber by the oscillatinggaseous flow from the combustors. This tangential movement will befollowed by downward movement due to the influence of gravity. It ispossible that some particles will remain suspended for periods of timenear pressure antinodes. FIGS. 3 and 4 illustrate the resultantgenerally inwardly falling spiral paths of travel. This results inlengthening the travel path of the particles in the processing chamberand increasing their residence times in the processing chamber, therebyincreasing the exposure time of the particles to the hot gases from thecombustor.

It should be understood that various types of materials may be processedby use of the present invention--gases, solids, powders, liquids, andvarious combinations thereof. In addition, it should be understood thatfor many applications a preferred method of processing such materialcomprises the step of optimizing the processing of material in thesystem, particularly by tuning to a frequency which optimizes aparticular parameter for a given process. For example, the optimizedparameter can include the final temperature of the processed material,the final moisture content of the processed material, the amplitude ofpulsations in the system to control noise level, the final chemicalcomposition of the processed material, and other parameters.

A particular application contemplated for the processing system 10 ofthe present invention is the cleaning of flue gases from boilers,incinerators, combustors and the like. Referring to FIGS. 1 and 12, fluegases to be cleaned are supplied to the processing chamber through inlet18. Reactants for cleaning the flue gas by chemical reactions aresupplied through supply pipe 16 and injected into the processing chamber12 through injectors 17. The tunable pulse combustors 14a and 14b excitepulsations within the processing chamber which enhance the rates ofchemical reactions between the flue gases and the reactants.

In a specific application of such a system for cleaning flue gases,sulfur dioxide (SO₂) are removed from the flue gases in the processingchamber 12. In this case the reactants comprise a mixture of lime ordolomite and water, or other suitable chemical reactants for flue gas,which upon injection into the processing chamber 12 will react with theflue gases introduced through the inlet 18 and remove all or most ofsulfur dioxide. Any particulates generated in these reactions such aspowder are collected as dried material 15 and removed by auger 22 orother material removing means. The cleaned flue gases are removedthrough the exhaust system 24 or by other gas removing means. It is tobe understood that other pollutants in flue gases, such as NO_(x), aswell as other types of gaseous materials and suspended materials, andother reactants capable of cleaning such other different gases or othermaterials, are contemplated for use in the present invention.

It should also be understood that the placement or location of theexciting means with respect to the process chamber 12 is not consideringlimiting of the present invention. For example, a pulse combustor orother acoustic exciting means may be mounted or positioned externally tothe processing chamber, yet still excite the various acousticoscillations in the processing chamber. For example, and referring toFIG. 12 by way of example and not by way of limitation to thisparticular embodiment, an acoustic exciter 19 such as a pulse combustormay be attached to the air inlet 18 as shown at 19a, to the exhaust port25 as shown at 19b, or to the removal system 22 as shown at 19c. In suchalternative configurations, the acoustic excitations produced by theexciter 19, even if spatially removed from the processing chamber 12,will still produce acoustic resonances in the processing chamberprovided that the frequency of excitation is properly selected andsufficient acoustic energy can propagate into the processing chamber tosustain resonance.

It will be appreciated that the processing chamber 12 in the system 10need not be stationary. The pulse combustor or other acoustic excitermay be attached to a rotating or other nonstationary processing chambersuch as a rotating kiln while still remaining within the scope of thepresent invention. For example, the configuration shown in FIG. 11, withthe pulse combustor 14h mounted along a longitudinal axis of theprocessing chamber 12, is particularly suitable for constructing asystem including a rotating processing chamber. It will of course beunderstood that the configuration of FIG. 11 is shown and describedbelow as being suitable for exciting longitudinal acoustic modes, but,as will be understood after the discussion on acoustics which follow,the configuration is not limited to longitudinal modes only.

ACOUSTIC MODES

In as much as the preferred embodiments of the present invention utilizenatural acoustic modes in the processing chamber to enhance the variousprocesses occurring therein, it is appropriate to next describe themethods by which such natural acoustic modes may be excited. It will benoted that the processing chambers 12 in the preferred embodiments aregenerally cylindrical; however, it should be understood that otherprocessing chamber geometrical configurations are also operable. Takingthe case of the generally cylindrical processing chamber, those skilledin the art will recognize that in solving wave equations for guides of acircular cross-section, Bessel and classical harmonic oscillatordifferential equations result. Accordingly, the solution for thepressure P' of a standing three-dimensional acoustic mode within thecylinder may be stated as:

    P'=[A cos lπy/L][cos mθJ.sub.m (S.sub.m,n r/R)]   (EQUATION 1)

where l=0, 1, 2, . . . (purely transverse modes occur for l=0);

A=the amplitude of the acoustic pressure oscillations;

y=the axial coordinate of the cylinder;

L=the length of a given cylinder;

θ=the transverse angular coordinate of the cylinder;

R=the radius of the given cylinder;

r=the radial coordinate of the cylinder;

where m=0, 1, 2, . . . (purely radial transverse modes occur for m=0 andl=0);

where n=0, 1, 2, . . . (purely tangential transverse modes occur for n=0and l=0); and

S_(m),n =the eigenvalues representing the solutions of the Besselfunction J'_(m) (x)=0.

FIGS. 1 and 2 illustrate the above coordinates and parameters. Thoseskilled in the art will also recognize that the acoustic resonanceinside a generally cylindrical processing chamber depends upon thegeometry of the cylinder, and the properties and the temperature of themedium inside the cylinder. The transverse mode frequency must satisfythe following equation: ##EQU1## where λ=wavelength;

ω=frequency;

R=radius of the cylinder;

T=temperature of the medium; ##EQU2## =velocity of sound in thecylinder; and γ=Cp/Cv=ratio of specific heats at constant pressure andconstant volume.

The natural frequencies of the three-dimensional modes are given by aformula which involves the constant S_(m),n given in Equation 2, theparameter l described in Equation 1, the length L of the processingchamber, and the acoustic boundary conditions at both ends of theprocessing chamber.

The natural frequencies of the longitudinal modes are given by a formulawhich depends upon the length L of the processing chamber and theacoustic boundary conditions of both ends of the processing chamber. Forexample, when both ends of the processing chamber are closed, thenatural frequencies of the longitudinal modes are given by the followingformula: ##EQU3## where l=1, 2, . . .

and those of the three-dimensional mode by: ##EQU4## where l=0, 1, 2 . ..

m=0, 1, 2 . . .

n=0, 1, 2 . . .

One consequence of Equations 2, 3 and 4, and the above discussion isthat the natural frequencies of the processing chamber depend upon theradius R and length L of the processing chamber, the average temperaturetherein and the constants S_(m),n and l which describe the excited mode.Similarly, the frequency of a pulse combustor depends upon the averagetemperature therein and a characteristic length, L_(c), such as, forexample, in systems incorporating the flame holder type pulse combustorsdescribed hereinbelow, the distance L_(c) between the flame holder andthe upstream end of the combustor. Thus, depending upon thecharacteristics of the excited processing chamber mode, thecharacteristic combustor length L_(c) can be larger or smaller than theradius R of the processing chamber. It is expected, however thatgenerally L_(c) ≧R when low frequency modes are excited and that L_(c)<R when higher frequency modes are excited.

It will therefore be understood by those skilled in the art that varyingL_(c) has the effect of varying the frequency of the pulse combustor andtherefore the frequency of excitation inside the processing chamber.

Another important observation is that while orientation of acousticexciting means influences the characteristics of the excitedoscillations, frequency of excitation is the predominant factor. Forexample, it should be apparent that tangentially directed pulses ofheated gases from pulse combustors are more likely to excite tangentialmodes than radial modes. However, because the internal acousticcharacteristics of the processing chamber, and not external influences,are determinative of the frequencies of the natural acoustic modes,provision of sufficient pulsating energy at the natural resonancefrequencies of desired modes of operation will generally excite themodes regardless of orientation of the exciting means.

As a practical matter, the acoustic modes of resonance will be detectedin the following manner. A microphone or other acoustic pick-uptransducer or detector should be attached to the exterior of theprocessing chamber, or on the interior if the temperature inside thechamber will not adversely affect the transducer. The chamber shouldthen be excited with suitable exciting means, as described herein. Theamplitude of acoustic excitation as detected by the transducer shouldthen be displayed as a function of frequency. As the frequency is variedover a range, maxima and minima of the amplitude will be observed; themaxima will indicate the frequencies of the natural modes of acousticresonance. Longitudinal, transverse and three-dimensional resonances maybe confirmed through a comparison with the expected resonancefrequencies, found through a theoretical analysis according to Equations1-4.

It will of course be understood that operation at a particular resonancemode will not necessarily be the end of the inquiry when preparing aparticular process for use in accordance with the present invention.Those skilled in the art will understand that optimization of someparameter of the process is the ultimate consideration. For example, inthe particular case of kaolin or food product drying, the moisturecontent of the end product is the parameter of interest. Other processeswill have other parameters of interest, for example, a chemical processmay have the concentration of a particular constituent compared to otherconstituents as the primary parameter of interest. Likewise, thetemperature of the end product being subjected to a process may beanother parameter of interest. Accordingly, to optimize a given processto take maximum advantage of the acoustic excitations being induced inthe processing chamber, it will be necessary to monitor the parameter ofinterest as a function of the frequency and amplitude of theoscillations.

As a particular example, it may be observed that the moisture content ofa product such as kaolin or food product reaches a desired level whenthe processing chamber is operated at a frequency of excitation whichdoes not exactly match one of the natural resonance modes. In accordancewith the invention, then, the process should be operated at theoptimization frequency for desired moisture content and not at aparticular resonance mode. The presence of pulsations in the processingchamber will still affect and enhance the process, notwithstanding thatthe desired end result or parameter is optimized at a frequencydifferent from one of the natural acoustic resonance modes of theprocessing chamber.

FIG. 2 provides instantaneous views of the pressure and flow streamlines at the beginning of a period of oscillation (time t=0) in FIG. 2Aand at the middle of the period (t=T/2) in FIG. 2B, for the firsttangential mode (n=0 in Equation 1). The pulse combustors 14a, 14b inFIG. 2 operate at the same frequency but in a phased relationship, andhave acoustic pressure distributions P'(x) upstream of the flame holdersimilar to the acoustic pressure P'(r) occurring inside the processingchamber 12. The exhaust outlets 30a, 30b of the pulse combustors alignwith a pressure nodal line 31, and the pulse combustors are mounted toexhaust heated gases along paths which at least initially are tangentialto the processing chamber wall 12.

As illustrated by the P'(r) curves in FIG. 2, which represent theinstantaneous pressure inside the processing chamber, the instantaneouspressure on the right side shifts from positive in FIG. 2A at time t=0,to negative in FIG. 2B at time t=T/2, every half cycle. It willtherefore be appreciated that a "sloshing" circumferential or circularmotion is imparted to the molecules of hot gases in the processingchamber 12, as the processing chamber is alternately supplied by pulsesof hot gases by each combustor 14a, 14b. It will, of course, beunderstood that synchronized out-of-phase operation is required toexcite this tangential mode in the configuration of FIG. 2, in thatin-phase operation would result in the creation of a continuousclockwise travelling acoustic mode in the processing chamber.

It should be generally understood that the pulse combustors shown in thesystems of FIGS. 1-11 may be of the type shown in FIGS. 15-20. In theparticular case of FIG. 2, the pulse combustors are tuned to apredetermined frequency to excite the first tangential mode, where S₁,0=1.84129. The frequency of operation of the tunable pulse combustorsshown in FIGS. 15-20 depends upon the length L_(c) between the flameholder 200 and the upstream end of the combustor tube 202. Accordingly,the length L_(c) should preferably be selected to be of the order of theradius of the dryer in order to successfully excite the first tangentialmode oscillations. In preferred embodiments, however, the pulsecombustors or other acoustic exciter should preferably be frequencytunable.

The tangential mode in FIG. 2 is considered a "standing" transverseacoustic mode, because the nodal line 32 is stationary and does notmove. It should, however, be understood that spinning transverse modes,where the nodal line 32 possesses an angular velocity, may also beexcited. For example, and as shown in FIG. 2B, imparting an angularvelocity to the nodal line results in motion in the direction of arrow34. Those skilled in the art will appreciate that angular movement ofthe nodal lines may be induced by synchronized operation of the pulsecombustors 14a, 14b at the same frequency with a predetermined phasedifference which is not equal to 180 degrees. Also, under certainconditions, a combination of a "standing" and spinning transverseacoustic modes may be excited in the processing chamber by variousarrangements of the pulse combustors 14a, 14b.

FIG. 5 illustrates the instantaneous pressure and flow stream linesoscillations for the first tangential mode of the processing chamber 12at the beginning of the period at time t=0, and midway through theperiod at time t=T/2. It may be observed from this figure that the"sloshing" type stream line oscillations characterize the firsttangential mode, while the acoustic pressure gradation lines intersectthe velocity nodal lines orthogonally.

It should be understood that in this example the "sloshing" typebehavior of the first tangential mode velocity field will exist in everytransverse plane of the processing chamber, inasmuch as longitudinal andradial modes are not deliberately excited, and l=0 and n=0 inEquation 1. In accordance with the present invention, the interaction ofthe acoustic resonance of the first tangential mode of the cylinder withmaterial to be processed in the processing chamber enhances the process.

It should also be understood that natural acoustic modes other than thefirst tangential mode may be excited by the system herein disclosed. Forexample, while FIG. 6A illustrates the first purely tangential mode asin FIG. 5, FIG. 6B illustrates the second tangential mode, where S₂,0=3.0543 in Equation 1, having pressure and flow stream lines diagrams asillustrated therein. It will also be understood and appreciated thatother higher tangential modes may also be excited, although as apractical matter the first and second will usually be the easiest toexcite and maintain.

In a similar manner, FIG. 7 illustrates purely radial modes ofoscillation, where l=0 and m=0 in Equation 1. In FIG. 7A, the pressure Pand flow stream lines V characteristic of the first radial mode areillustrated, for S₀,1 =3.8317. FIG. 7B illustrates the second radialmode, for S₀,2 =7.0156. Again, other higher order radial modes are alsocontemplated in the present invention, but the first and second modesare believed to be of the most practical utility.

It should also be understood that other transverse acoustic modes withmotions consisting of combinations of radial and tangential oscillationsare also contemplated in the present invention. For example, thetransverse mode characterized by l=0, m=1, and n=1 in Equation 1 is sucha combined tangential-radial mode. In a similar manner, FIG. 8illustrates purely longitudinal modes of oscillation, where m=0 and n=0in Equation 1. In FIG. 8A, the pressure P and flow stream lines Vcharacteristic of the first longitudinal acoustic mode, where l=1 inEquation 1, are illustrated. The frequency of this mode equals C/2LHertz (Hz.). FIG. 8B illustrates the pressure P and flow stream lines Vof the second longitudinal mode, where l=2 in Equation 1, having afrequency of C/L Hz. Again, higher order longitudinal modes are alsocontemplated in the present invention, but the lowest longitudinal modesare believed to be of the most practical utility.

A combination of a particular transverse mode and a particularlongitudinal mode may be considered a three-dimensional mode, due to thefact that three-dimensional acoustic modes may be decomposed into theirtransverse components and longitudinal components. This fact is apparentin Equation 4 which shows that the frequency of a three-dimensional modeis proportional to the frequencies of the transverse and longitudinalmodes. Accordingly, it will be understood that deliberate excitation ofparticular three-dimensional acoustic resonances in the processingchamber is within the scope of the present invention.

It should also be understood that excitation of longitudinal modessimultaneously with transverse modes may inevitably occur when thefrequencies of one or more longitudinal and/or transverse modes aresmaller than the frequency of the excited transverse orthree-dimensional mode. For example, assume that for a given processingchamber, it is desired to excite the first tangential mode, and that thefrequency required to excite this mode is 600 Hertz (Hz). Assume furtherthat the natural frequencies of the first four longitudinal modes arebelow 580 Hz. Due to the differences between these frequencies,excitation of the first tangential mode could simultaneously excite oneor more of the four longitudinal modes in this example. It willtherefore be understood that operation with simultaneous excitation ofseveral acoustic modes are contemplated in the present invention.Specifically, all natural acoustic modes of the processing chamberhaving frequencies smaller than the frequency of the excited mode couldbe excited and be present in the processing chamber together with theexcited mode. For example, the first longitudinal mode could be excitedwhen any transverse or three-dimensional mode is excited.

METHODS FOR EXCITING NATURAL ACOUSTIC MODES

FIGS. 9-11 illustrate orientation of combustors or other excitationmeans to excite various acoustic modes in the processing chamber 12. Ofcourse, it will be recalled that the configuration shown in FIG. 2 maybe employed to excite tangential and other modes. In addition, and asshown in FIG. 9, a tandem pair of parallel, aligned combustors 14c, 14dcan be tangentially connected to opposite tangents of the processingchamber 12 and operated in phase in order to excite tangentialoscillations. Analogous to the case of FIG. 2, out-of-phase operation ofthe parallel tandem combustors 14c, 14d would result in a spinningmotion of the first tangential mode in the processing chamber. It is tobe understood that tandem or other placements of one or more pulsecombustors may be used to excite the first tangential mode of theprocessing chamber.

FIG. 10 illustrates placement of combustors 14e, 14f, and 14g to exciteone of the radial modes of the processing chamber 12. As shown in FIG.10, combustors 14e, 14f, and 14g are mounted aligned with the radii ofthe generally cylindrical processing chamber 12 so that the exhaustoutlets 30e, 30f, and 30g are tangential to the circular acousticpressure nodal line 35 of the excited radial mode. Additional pulsecombustors installed in a manner similar to that of combustors 14e, 14f,and 14g may be added if additional energy input and/or larger pulsationamplitudes are required in the processing chamber 12. Finally, otherpure radial modes of the processing chamber 12 may be excited by usingpulse combustors having the same frequency as that of the mode to beexcited and positioning their exhaust exit planes tangential to one ormore circular acoustic pressure nodal lines of the mode to be excited.

Referring next to FIG. 11, mounting of a combustor 14h so that theexhaust outlet 30h is positioned at a distance L/2, where the totallength of the processing chamber 12 is L, tends to excite thefundamental longitudinal mode of oscillation.

It should also be understood that the excitation of three-dimensionalacoustic modes of the processing chamber by use of similar excitationmethods is contemplated in the present invention. In the contemplatedconfigurations, the exit planes of one or more pulse combustors will bealigned tangentially with one or more velocity anti-nodal surfaces ofthe mode to be excited, and the pulse combustors will be operated withthe frequency of the mode to be excited.

As has been described above, the preferred embodiments employ tunablepulse combustors for exciting desired acoustic modes. However, it shouldbe understood that various means for producing acoustic excitations inthe processing chamber 12 may be successfully employed to excite theacoustic modes. Tunable pulse combustors suitable for use as excitationmeans are illustrated in FIGS. 15-20 and described herein below. Othersuitable excitation means will be described next.

FIG. 12 illustrates another technique for exciting acoustic modes in theprocessing chamber 12. In the embodiment 10" shown in FIG. 12, materialto be dried is provided through the supply line 16 as in the embodimentof FIG. 1. However, a different combustor design 202 is utilized tosupply the hot gas flow and excite the acoustic mode oscillations in theprocessing chamber 12. The combustor 202 of the illustrated embodimentis attached to the processing chamber 12 at a location above the wetmaterial injection nozzles 17. The combustor 202 includes one or moreair inlet ports 204, fuel injection orifices 203, a centerbody 205 forsupporting the disc flame holder 200, and for supplying additional fuelthrough orifices 206, and an igniter 207. The centerbody is translatablealong directions shown by arrows 225.

Upon ignition, combustion occurs in vortices 209 which form inside theshear layers 210 and 211 located downstream of the disc flame holder 200and the combustor-processing chamber interface 212. The combustionprocesses inside these vortices are unsteady and excite one or more ofthe natural acoustic modes of the processing chamber 12. The type ofexcited mode and its amplitude may be controlled by axial translation ofthe centerbody 205 and/or changing the diameter of the flame holder 200or combustor 202. It is to be understood that in the present embodimentthe combustion process within the shear layers can occur within thecombustor 202, the processing chamber 12, or both. Also, the inventionis not restricted to the use of disc shaped flame holders; flame holdershaving conical, rod-like, gutter-like, and other configurations arecontemplated within the scope of this invention because such flameholders can also excite desired acoustic oscillations within theprocessing chamber 12 as long as they are capable of producing the shearlayers and the reacting vortices having the desired properties.

Turning now to FIG. 13, another method for exciting natural acousticmode oscillations inside the processing chamber 12 is illustrated, witha fuel modulator 125. Air is supplied through pipe 121 which connects tothe processing chamber 12. Fuel is supplied through a fuel line 124 intoa fuel flow modulator 125, which modulates the flow of fuel through pipe126 into the pipe 121 to provide a combustible mixture inside pipe 121whose composition changes periodically in time with the frequency offuel modulation. The combustible mixture is delivered to the processingchamber where it is burned in the vicinity of the interface between pipe121 and the processing chamber 12. Because the composition of thecombustible mixture varies periodically with time, the reaction rate isalso periodic. This results in the excitation of acoustic pulsationsinside the processing chamber 12. By matching the frequencies of thefuel flow modulation and the reaction rate with the frequency of one ofthe natural acoustic modes of the processing chamber, the periodiccombustion process will excite this mode and, possibly, excite othermodes within the processing chamber.

FIG. 14 illustrates a preferred embodiment of the fuel flow modulator125 employed in the system of FIG. 13. The fuel flow modulator 125comprises a fixed fuel inlet pipe or sleeve 135 connected to receive aflow of fuel from fuel line 124, and a concentric rotating sleeve 130positioned on the exterior of the inlet pipe 135. The fixed sleeve 135includes a plurality of orifices 131 positioned diametrically around acircumference of the pipe. The rotating sleeve 130 also includes asimilar plurality of orifices 136 which are radially alignable opposingthe orifices 131 in the fixed sleeve.

The rotating sleeve 130 is affixed to an idler gear 140, which is drivenby a drive gear 141. A shaft 142 connected to a motor M₄ is providedthrough a bushing 143 in the side wall of the fuel flow modulator 125.It will be appreciated that the speed of rotation of motor M₄ controlsthe speed of rotation of the rotating sleeve 130, thereby controllingthe frequency of modulation of fuel flow. It will also be appreciatedthat the rotation of the rotating sleeve 130 periodically interrupts theflow of fuel introduced through the fuel inlet pipe 124, so that thefuel flow exciting the modulator 125 via the fuel pipe 126 is modulatedas a function of the speed of rotation of the rotating sleeve 130.

IMPROVED PULSE COMBUSTORS

Turning next to FIGS. 15-20, the pulse combustors 14a-f of FIGS. 15-20are particular preferred embodiments of pulse combustors constructed inaccordance with the present invention. These pulse combustors are notnecessarily the same as the pulse combustors 14a-g of FIGS. 1-3 and9-10. However, it should be understood that the systems shown in theselatter figures may be constructed with the pulse combustors of FIGS.15-20.

FIG. 15 illustrates a preferred embodiment of a tunable pulse combustor14a which can be used to excite longitudinal, transverse andthree-dimensional acoustic modes in the processing chamber of thepresent invention. The pulse combustor 14a comprises a combustor tube202 (which generally consists of a straight pipe), and a centerbody 205which supports a disc shaped flame holder 200. The centerbody 205 is arod or tube containing a plurality of fuel injection orifices 206 whichsupply part or all of the required fuel. Air for combustion is suppliedthrough inlet pipe 204 into an upstream acoustic decoupler 213 whichcommunicates with the upstream end of the combustor tube 202. Thedecoupler 213 minimizes the propagation of pulsations into the airsupply pipe 204. All or part of the needed fuel can be supplied throughorifices 203 located in the outer combustor wall in the vicinity of theflame holder 200. To start the combustor 14a, a combustible mixture isignited by the ignitor 207. Subsequently, unsteady combustion occursinside the vortices 209 which form inside the shear layer 210 downstreamof the flame holder 200. These unsteady combustion processes excitenatural acoustic oscillations in the combustor tube 202 upstream of theflame holder 200. The frequency of these oscillations is determined bythe length L_(c) between the flame holder 200 and the upstream decoupler213. In the embodiment illustrated in FIG. 15 the length L_(c) will beapproximately equal to half the wavelength of the excited pulsationswhose frequency f is determined by the following equation:

    f=L.sub.c /(2C)                                            (EQUATION 5)

where C is the speed of sound.

As discussed above, the frequency of pulsations can be changed bychanging the length L_(c). The embodiment shown in FIG. 15 changes thelength of the combustor tube 202 with a sleeve-type arrangement 214and/or axial translation of the centerbody 205 which moves the locationof flame holder 200. The upstream decoupler 213 with the sleeve 214 canmove longitudinally along arrows 226 to change the length L_(c) betweenthe decoupler 213 and the flame holder 200. Similarly, longitudinaltranslation of the centerbody 205 along arrows 225 changes the lengthL_(c).

It is to be understood that in the embodiment shown in FIG. 15, acousticpulsations will not be restricted to the region upstream of the flameholder. Pulsations will also be excited in the combustor tube sectiondownstream of the flame holder 200, and/or in a system attached to thedownstream end of the combustor such as, for example, the processingchamber 12.

Additional means for controlling the range of acoustic frequencies whichcould be excited by combustor 14a include changing the diameter of thecombustor tube 202, the diameter of the flame holder 200, and the ratioof the flame holder diameter and combustor tube diameter. It is also tobe understood that decreasing the combustor tube diameter will generallyincrease the magnitudes of the excited frequencies.

Another preferred embodiment of a tunable pulse combustor 14b is shownin FIG. 16. In this embodiment combustion air is supplied through an airinlet pipe 204 located just downstream of the closed upstream end 215 ofthe combustor tube which requires that the acoustic velocity there bezero. Consequently, in the embodiment of FIG. 16 the length L_(c)between the flame holder 200 and the upstream termination 215 will equalone quarter of the wavelength of the excited acoustic oscillation andthe resulting frequency f will equal:

    f=L.sub.c /(4C)                                            (EQUATION 6).

Examination of the above equation shows that the frequency of pulsationscan be controlled by changing the length L_(c) shown in FIG. 16. Thiscan be accomplished by moving the termination 215 along arrows 227, thecenterbody 205 and flame holder 200 along arrows 225, or both. Thecenterbody 205 is a rod or tube extending along the longitudinal axisthrough an aperture in the upstream end of the combustor tube. Again, asin the embodiment of FIG. 15, the pulsations in the embodiment of FIG.16 are excited by unsteady combustion processes inside vortices 209which form inside the shear layer 210 downstream of the flame holder200.

FIG. 17 illustrates another preferred embodiment of a tunable pulsecombustor 14c which excites acoustic mode oscillations in a processingchamber. The pulse combustor 14c includes a combustion chamber 229 whichis comprised of a straight cylindrical pipe 228 connected to aconvergent pipe section 216 which connects to a tail pipe 217 at itsdownstream end. The tail pipe 217 is used to exhaust the combustionproducts from the combustor 14c and to serve as a wave guide throughwhich the pulsations propagate to other systems which may be attached tothe pulse combustor 14c such as, for example, the processing chamber 12.Air for combustion is provided through the air inlet 204 which may beL-shaped, although it could be bent into any other convenient shape. Thediameter of the air inlet pipe 204 is smaller than the diameter of theinitial combustor section 228. As a result, a recirculation region,where combustion occurs, is formed in the corner region 218. Thisrecirculation region 218 serves as an ignition source for fresh chargesof fuel and air which continuously enter the combustor.

Fuel for combustion is supplied through at least one injection orifice203 which may be located either in the air inlet wall just upstream ofthe combustor, and/or at the interface of the air inlet with thecombustor. Fuel can also be supplied through orifices 206 in thecenterbody 205. A disc shaped flame holder 200 is attached to thedownstream end of the centerbody 205. The flow of the air and fuel pastthis flame holder 200 results in the formation of a shear layer 210downstream of the flame holder. An additional shear layer 211 is formeddownstream of the interface between the combustor 214 and the air inlet204. Unsteady combustion occurs inside vortices 209 which form insidethese shear layers. These unsteady combustion processes excite acousticoscillations in the air inlet, the combustor and any system which may beattached to the downstream end of the tail pipe 217.

In the embodiment shown in FIG. 17, the frequency and amplitude of theexcited pulsations can be controlled by axial translation of the flameholder 200 along arrows 225 within the combustor, changing the diameterof the disc flame holder, and changing the combination and locations offuel orifices used to inject a given amount of fuel into the combustor.It should be also pointed out that the use of other flame holdergeometries such as a cone, a ring and the like are also contemplated.

FIG. 18 illustrates another preferred embodiment of a tunable pulsecombustor 14d which can be used to excite longitudinal, transverse andthree-dimensional acoustic modes in a processing chamber according tothe present invention. The pulse combustor 14d includes a combustor tube202 which comprises a straight pipe and a centerbody 205 attached to adisc shaped flame holder 200 at its downstream end. An additionalannular flat ring or large orifice type flame holder 219 is attached tothe outer combustor wall in the vicinity of the location of the flameholder 200. The centerbody 205 contains at least one fuel injectionorifice 206 which supplies part or all of the required fuel. Another setof orifices 203, located in the outer combustor wall in the vicinity ofthe flame holders 200 and 219, can be used to supply all or part of theneeded fuel. Air for combustion enters the upstream decoupler 213through inlet pipe 204. The upstream decoupler is connected to theupstream end of the combustor tube 202 by a sleeve-type connection 214which provides a capability for lengthening or shortening the combustorby moving the sleeve along arrows 226.

Unsteady combustion occurs inside vortices 209 which are transported bythe gas flow inside the shear layers 210 and 211 formed downstream ofthe flame holders 200 and 219. These unsteady combustion processesexcite longitudinal acoustic oscillations in the combustor tube 202upstream of the disc flame holder 200. The frequency of theseoscillations is determined by the length L_(c) between the flame holder200 and the upstream decoupler 213. In the embodiment shown in FIG. 18,the length L_(c) approximately equals half the wavelength of the excitedacoustic oscillations whose frequency f is determined by Equation 5above.

FIG. 19 illustrates another embodiment of a tunable pulse combustor 14ewhich can be used to excite longitudinal, transverse andthree-dimensional acoustic modes in the processing chamber of thepresent invention. The combustor tube 202 of the pulse combustor 14ecomprises a straight pipe. The combustor tube 202 connects to theupstream decoupler 213 via a sleeve-type arrangement 214, which providesmeans for changing the length of the combustor 202 by moving the sleevealong arrows 226. The combustor 14e includes a centerbody 205 which isattached to a disc shaped flame holder 200 at its downstream end. Anadditional, circular, ring shaped, flame holder 221 is attached, viathin rods 223, to the outer combustor wall in the vicinity of thedownstream end of the centerbody 205. The thin rods 223 are standardswhich displace the annular flame holder from the wall of the combustortube. The flame holder 200 can be moved relative to the annular flameholder 221 by moving the centerbody 205 along arrows 225.

The centerbody 205 in the embodiment of FIG. 19 contains fuel injectionorifices 206 which supply part or all of the required fuel. All or partof the needed fuel can be also supplied through an additional set oforifices 203 located in the outer combustor wall in the vicinity of theflame holder 221. Air for combustion is supplied through an inlet pipe204 into the upstream decoupler 213 which is connected to the upstreamend of the combustor tube 202.

Unsteady combustion occurs inside vortices 209 which are transported bythe flow inside shear layers 210 and 211 which form downstream of theflame holders 200 and 221. These unsteady combustion processes excitelongitudinal acoustic oscillations in the combustor tube upstream of theflame holders 200 and 221. The frequency of these oscillations isdetermined by the length L_(c) between the flame holders and theupstream decoupler 213. In the embodiment shown in FIG. 19, the lengthL_(c) approximately equals half the wavelength of the excited acousticoscillations whose frequency f is determined by Equation 5 above.

FIG. 20 illustrates yet another preferred embodiment of a tunable pulsecombustor 14f which can be used to excite longitudinal, transverse andthree-dimensional acoustic modes in the processing chamber of thepresent invention. The straight pipe combustor tube 202 connects to theupstream decoupler via a sleevetype arrangement 214, which provides ameans for changing the length of the combustor 202 by moving the sleeve214 along arrows 226. The combustor includes a centerbody 205 which isattached, via thin metal rods 222, to a ring shaped flame holder 220 atits downstream end. An additional, ring shaped flame holder 221 isattached, via thin rods 223, to the outer combustor wall in the vicinityof the downstream end of the centerbody 205. The flame holder 220 can bemoved relative to the flame holder 221 by moving the centerbody 205along the combustor in the directions of arrows 225.

An end view of the two ring shaped flame holders 220 and 221 shown inFIG. 20 is provided in FIG. 21.

The centerbody in the embodiment of FIG. 20 contains fuel injectionorifices 206 which supply part or all of the required fuel. All or partof the needed fuel can be also supplied through an additional set oforifices 203 located in the outer combustor wall in the vicinity of theflame holder 221. Air for combustion is supplied through an inlet pipe204 into an upstream decoupler 213 which is connected to the upstreamend of the combustor tube 202.

Unsteady combustion occurs inside vortices 209 which are transported bythe flow inside shear layers 210 and 211 which form downstream of thering-like flame holders 220 and 221. These unsteady combustion processesexcite longitudinal acoustic oscillations in the combustor tube upstreamof the ring-like flame holders 220 and 221. The frequency of theseoscillations is determined by the length L_(c) between the flame holdersand the upstream decoupler 213. In the embodiment shown in FIG. 20 thelength L_(c) approximately equals half the wavelength of the excitedacoustic oscillations whose frequency f is determined by Equation 5above.

In the pulse combustor embodiments shown in FIGS. 18, 19 and 20, thefrequency of pulsations can be changed by changing the length L_(c)between the flame holders and the upstream decoupler 213. This can beaccomplished by changing the length of the combustor tube 202 by movingthe sleeve-type arrangement 214 along the directions given by arrows 226and/or by changing the position of the flame holders which are locatedon the centerbody 205, by moving the centerbody 205 along the directionsof arrows 225.

It is also to be understood that in the embodiment shown in FIGS. 18, 19and 20, acoustic pulsations will not be restricted to the regionupstream of the flame holders and they could also be excited,simultaneously, in the combustor tube section downstream of the flameholders, and/or in a system which is attached to the downstream end ofcombustor such as, for example, the processing chamber 12 considered inthe present invention.

Additional means for controlling the range of acoustic frequencies whichcould be excited by the tunable pulse combustors embodiments shown inFIGS. 15-20 include: changing the diameter of the combustor tube,changing the diameters of the flame holders, and changing the ratios ofthe flame holder diameters to the combustor tube diameter. It is also tobe understood that decreasing the combustor tube diameter will generallyincrease the magnitudes of the excited frequencies.

It is also to be understood that the pulse combustor embodiments shownin FIGS. 18, 19 and 20 can be modified without any adverse effects byreplacing the decoupler 213 at their upstream end with a "hardtermination" or acoustically closed end similar to the one shown at 215at the upstream end of the tunable pulse combustor configuration shownin FIG. 16. In the modified configuration, the distance L_(c) betweenthe flame holders and the "hard wall" upstream termination willgenerally equal one quarter of the wavelength of pulsations whosefrequency f will be given by Equation 6 above.

It will be understood that any geometric configuration or other meanswhich produce interacting shear layers is considered a "flame holder"for purposes of the present invention. It will thus be understood thatthe disc or ring shaped flame holders shown in the embodiment of FIGS.15-20 can be replaced by other types of flame holders such as aconfiguration where the centerbody or rod 205 terminates without alarger-diameter disk, a cross-shaped or other multi-rod configuration, aconical flame holder such as shown at 230 in FIG. 22, a "gutter" typeflame holder, and the like. Similarly, the ring shaped flame holders canbe replaced by flame holders having non-circular shapes such as, forexample, diamond-like shapes.

The preferred embodiments of the present invention have been disclosedby way of example and it will be understood that other modifications mayoccur to those skilled in the art without departing from the scope andthe spirit of the appended claims.

What is claimed is:
 1. A frequency tunable pulse combustor, comprising:a combustion chamber; a rod extending into said combustion chamber; a disk shaped flame holder attached to an end of said rod for forming at least one reacting shear layer region which excites pulsations in said combustion chamber; a combustion zone operatively associated with said combustion chamber wherein a combustion reaction of fuel and air occurs in said shear layer region and heat is released to excite pulsations inside said tunable pulse combustor; a circular ring flame holder affixed to a wall of said combustion chamber for forming a second reacting shear layer region to excite pulsations in said combustor; a decoupler having an interfitting sleeve coaxial with said combustion chamber for supplying air into said combustion zone for said combustion reaction; fuel supply means for supplying fuel into said combustion zone for said combustion reaction; exhaust means for exhausting combustion by-products; and adjusting means for selectively changing the frequency of pulsations in said shear layer regions, thereby providing a selectively frequency tunable pulse combustor.
 2. The frequency tunable pulse combustor of claim 1, wherein said adjusting means comprises means for axially translating said rod with respect to said combustion chamber.
 3. The frequency tunable pulse combustor of claim 1, wherein said adjusting means comprises means for axially translating said decoupler with respect to said combustion chamber.
 4. A frequency tunable pulse combustor, comprising:a combustion chamber having a closed upstream end; flame holder means for forming at least one reacting shear layer region which excites pulsations in said combustor; a combustion zone operatively associated with said combustion chamber wherein a combustion reaction of fuel and air occurs and heat is released to excite pulsations inside said tunable pulse combustor; air intake means positioned proximate said closed end for supplying air into said combustion zone for said combustion reaction; fuel supply means for supplying fuel into said combustion zone for said combustion reaction; exhaust means for exhausting combustion by-products; and adjusting means for selectively varying the frequency of pulsations in tunable pulse combustor, thereby providing a selectively frequency tunable pulse combustor.
 5. The frequency tunable pulse combustor of claim 4, wherein said adjusting means comprises means for axially translating said flame holder means with respect to said combustion chamber.
 6. The frequency tunable pulse combustor of claim 4, wherein said adjusting means comprises means for axially translating said closed end of said combustion chamber with respect to said combustion chamber.
 7. The frequency tunable pulse combustor of claim 4, wherein said flame holder means comprises a longitudinal rod and a flame holder attached to the downstream end of said rod.
 8. The frequency tunable pulse combustor of claim 7, wherein said flame holder comprises a disk.
 9. The frequency tunable pulse combustor of claim 7, wherein said flame holder comprises a cone.
 10. The frequency tunable pulse combustor of claim 7, wherein said flame holder comprises a ring.
 11. The frequency tunable pulse combustor of claim 7, wherein said flame holder is a first flame holder, and further comprising second flame holder means for forming a second shear layer region which excites pulsations in said combustor.
 12. The frequency tunable pulse combustor of claim 11, wherein said second flame holder means comprises a circular ring flame holder affixed to the wall of said combustion chamber.
 13. The frequency tunable pulse combustor of claim 11, wherein said adjusting means comprises means for axially translating said first flame holder means with respect to said second flame holder means.
 14. An improved pulsating processing system for conducting a process in a pulsating environment, comprising:a processing chamber for processing material; means for introducing material to be processed into said processing chamber; means operatively associated with said processing chamber for introducing a flow of reactants into said processing chamber to process material introduced into said processing chamber, said flow of reactants producing a reaction in said processing chamber; means for exciting at least one natural acoustic mode in said processing chamber, said exciting means being operative about the frequency of a natural acoustic mode of said processing chamber; tuning means operatively associated with said processing chamber and said exciting means for selecting the frequency of said exciting means about the frequency of said natural acoustic mode; exhaust means for exhausting reaction by-products from said processing chamber; and means for removing processed material from said processing chamber, whereby material introduced into said processing chamber is subjected to acoustic pulsations about the frequency of said natural acoustic mode while the material is being processed in said processing chamber.
 15. The pulsating processing system of claim 14, wherein said system is a heat transfer system.
 16. The pulsating processing system of claim 15, wherein said heat transfer system is a heater.
 17. The pulsating processing system of claim 15, wherein said heat transfer system is a boiler.
 18. The pulsating processing system of claim 14, wherein said system is a chemical processing system.
 19. The pulsating processing system of claim 18, wherein said chemical processing system is a calcining system.
 20. The pulsating processing system of claim 18, wherein said material to be processed is a gas, and wherein said chemical processing system is a system for containing a gaseous chemical reaction wherein at least one of the reactants is a gas.
 21. The pulsating processing system of claim 20, wherein said gas is flue gas from a combustion process, and wherein said reactants comprise chemicals for reacting with said flue gas.
 22. The pulsating processing system of claim 14, wherein said system is a physical processing system.
 23. The pulsating processing system of claim 22, wherein said physical processing system is a material drying system.
 24. The pulsating processing system of claim 23, wherein said material drying system is a kaolin drying system.
 25. The pulsating processing system of claim 23, wherein said material drying system is a food drying system.
 26. The pulsating processing system of claim 14, wherein said natural acoustic mode is a longitudinal mode.
 27. The pulsating processing system of claim 14, wherein said natural acoustic mode is a transverse acoustic mode.
 28. The pulsating processing system of claim 14, wherein said natural acoustic mode is a three-dimensional acoustic mode.
 29. The pulsating processing system of claim 14, wherein said exciting means and said tuning means comprises a tunable pulse combustor.
 30. The pulsating processing system of claim 14, wherein said exciting means comprises means for modulating the flow of reactants introduced by said reactant introducing means, and said tuning means comprises means for controlling the frequency of modulation of said reactant modulating means.
 31. The pulsating processing system of claim 30, wherein said modulating means comprises fuel flow modulating means.
 32. The pulsating processing system of claim 14, wherein said reactant flow comprises a flow of fuel and air, and wherein said reaction is a combustion reaction.
 33. The pulsating processing system of claim 14, wherein said exciting means comprises flame holder means for forming at least one reacting shear layer region which excites plusations in said processing chamber.
 34. The pulsating processing system of claim 33, wherein said tuning means comprises means for axially translating said flame holder means.
 35. The pulsating processing system of claim 33, wherein said flame holding means comprises a disk positioned in said processing chamber.
 36. The pulsating processing system of claim 33, wherein said flame holding means comprises a cone positioned in said processing chamber.
 37. The pulsating processing system of claim 33, wherein said flame holding means comprises an annular ring positioned in said processing chamber.
 38. The pulsating processing system of claim 33, wherein said flame holding means is a first flame holding means, and further comprising a second flame holding means for forming a second reacting shear layer region which excites pulsations in said processing chamber.
 39. The pulsating combustion system of claim 38, wherein said second flame holding means comprises an annular ring positioned inside said processing chamber.
 40. The pulsating processing chamber of claim 38, wherein a cross-sectional dimension of said processing chamber is greater than a corresponding cross-sectional dimension of said reactant flow introducing means, thereby forming said second reacting shear layer region inside said processing chamber.
 41. A method of processing material by subjecting the material in a processing chamber to a pulsating processing environment, comprising the steps of:(1) introducing material to be processed into said processing chamber; (2) providing a pulsating flow of heated gases at a selected frequency to said processing chamber to process said material; and (3) tuning said frequency to a frequency about a natural acoustic mode of said processing chamber, whereby material introduced into the processing chamber is subjected to acoustic pulsations about the frequency of a natural acoustic mode of the processing chamber while the material is being processed in the processing chamber.
 42. The method of claim 41, further comprising the step of optimizing the processing of material in said processing chamber by tuning to a frequency which optimizes a particular parameter for a given process.
 43. The method of claim 42, wherein the optimized parameter is the final temperature of the processed material.
 44. The method of claim 42, wherein the optimized parameter is the final moisture content of the processed material.
 45. The method of claim 42, wherein the optimized parameter is the amplitude of pulsations inside the processing chamber to reduce noise level.
 46. The method of claim 42, wherein the optimized parameter is the final chemical composition of the processed material. 